EELS Studies of materials for solid-state battery - On the
limitation of TEM/STEM toward quantification

Nan Jiang

Department of Physics

Arizona State University

Tempe, AZ 85287-1504

Radiation damage remains an important obstacle to extend applications of
(scanning) transmission electron microscopy (TEM/STEM). Aberration correction
allows the STEM objective aperture (condenser aperture in TEM nanodiffraction
mode) to be enlarged so that the electron probe on the specimen may have a very
high current density, e.g. > 106 A/cm2. This value is
about 104 – 105 times larger than the current density used
in forming conventional HREM images, and about 106 – 107
larger than that used for bright-field diffraction contrast imaging. Can
materials survive under these conditions?

The materials for solid-state batteries are very good conductors of ions
but are essentially insulating toward electrons. These materials usually contain
mobile ions such as Ag+, Li+, Na+ or H+
for conduction. These features ensure that they are all susceptible to
high-energy electron irradiation, and can be damaged or modified easily by the
electron beam. But how serious this problem could be and how to avoid it? Based
on extensive electron energy-loss spectroscopy (EELS) studies in various Li
compounds, we are able to identify the dominant mechanism responsible for their
susceptibility to electron beam in this group of materials. The commonly
recognized knock-on and radiolysis play only a minor role, compared with the
electron irradiation induced electric field. Driven by the induced electric
field, the damages vary from the long-range Li migration over a distance larger
than several microns to the short-range migration leading to the relocation of
Li in different lattice sites. The commonly used ways to eliminate or reduce
damage, such as lowering beam voltage, lowering specimen temperature and coating
with protection films, may not help due to the nature of damage mechanism.
Instead, a feasible approach within the currently available technologies is
lowering the beam current, but giving up spatial resolution perhaps.